1. Field of the Invention
The present invention relates to a polycrystalline silicon reactor to be used when producing polycrystalline silicon by the Siemens method.
Priority is claimed on Japanese Patent Application No. 2008-074469, filed Mar. 21, 2008, the content of which is incorporated herein by reference.
2. Description of Related Art
The Siemens method is known as a method of producing high-purity polycrystalline silicon to be used as a semiconductor material. This Siemens method is a production method of bringing a source gas composed of a mixed gas of chlorosilanes and hydrogen into contact with a heated silicon seed rod, and depositing the polycrystalline silicon on the surface of the seed rod by reaction of the source gas. As an apparatus which carries out this production method, a polycrystalline silicon reactor in which many silicon seed rods are stood is used. Generally, the silicon seed rods are connected by a connecting member at upper ends thereof to form in a Π-shape, and both lower ends thereof are fixed to electrodes which are installed at a furnace bottom of the reactor.
Thus, an electric current is applied to the whole silicon seed rods from the electrodes located at both ends, and the whole silicon seed rods are heated to about 1050° C. to 1100° C. which is the thermal decomposing temperature of the source gas by Joule's heat by the electric current. The source gas supplied into the furnace contacts the surfaces of the silicon seed rods heated in this way, and is thermally decomposed or hydrogen-reduced, whereby polycrystalline silicon is deposited on the surfaces of the silicon seed rods. As this reaction proceeds continuously, rod-like polycrystalline silicon grows up (for example, refer to Japanese Patent No. 2867306).
Meanwhile, in the process during which a source gas of chlorosilanes, such as trichlorosilane, reacts within the furnace, and polycrystalline silicon deposits on the surfaces of the silicon seed rods, the weight of the polycrystalline silicon which has been deposited on the electrodes reaches to tens of kilograms by continuing the reaction. Therefore, the silicon may be peeled off from the electrodes due to its own weight, and may damage the furnace bottom of the reactor. In addition, the peeled-off polycrystalline silicon may cause a hindrance to continuation of the reaction, for example, by causing short-circuiting between the electrodes and the furnace bottom.